WO1998056018A2

WO1998056018A2 - Planar inductive devices

Info

Publication number: WO1998056018A2
Application number: PCT/IL1998/000252
Authority: WO
Inventors: David Schneider
Original assignee: Planex Ltd.
Priority date: 1997-06-02
Filing date: 1998-05-29
Publication date: 1998-12-10
Also published as: IL120980A0; WO1998056018A3; AU7546498A

Abstract

A planar inductive device (32) comprising: at least one substrate board (34) having planar windings formed thereon; and a core (36), arranged with respect to the windings, so as to form a magnetic path between the windings, wherein the at least one board is provided with contact connectors (46, 48) on an edge thereof for edge mounting the at least one board.

Description

PLANAR INDUCTIVE DEVICES

FIELD OF THE INVENTION The present invention relates to planar inductive devices and in particular to methods of constructing planar inductive devices and attaching them to printed circuit boards. BACKGROUND OF THE INVENTION

Planar transformers, planar inductors, and other planar inductive devices, hereinafter planar inductive devices are inductive devices in which conductors forming the windings of the inductive devices, in the form of spirals, are formed on or in thin flat insulating substrates. The conductors are formed using various processes known to the art but most often by etching the desired conducting pattern on a thin insulating substrate board, such as a printed circuit board, using the techniques and materials commonly employed in the production of such boards.

A planar inductive device can be constructed using only a single substrate board with appropriate conductor patterns. Generally, however, a multiplicity of substrate boards are stacked together to form a thin substrate stack with winding conductors on the boards appropriately interconnected to complete the windings of the planar inductive device. The boards are formed with matching apertures which are aligned when the boards are stacked together. The apertures allow for the insertion of a magnetic, preferably ferrite, cores into the windings to provide a magnetic circuit for the planar inductive device. In the prior art, the planar inductive device is mounted on a printed circuit board with the plane of the substrate stack parallel to the plane of the circuit board. In this mounting disposition, extension leads are provided to make electrical contact between the windings of the planar inductive device and the circuit board. The extension leads are connected to contact points near to the edges of the boards which are connected to the windings. Fig. 1 shows a conventional planar transformer 20 mounted on a printed circuit board

200. Transformer 20 includes a stack 22 of substrate boards on which the transformer windings (not shown) are formed. The substrate boards are parallel to the plane of printed circuit board 200. A ferrite core 24, formed of two mating parts 26 and 28, sandwiches stack

22. The thickness of the core displaces the stack from the circuit board and extension leads 30 are provided to electrically connect the transformer windings to circuit board 200.

The construction and mounting of conventional planar transformers are described in the literature and in the publications of commercial companies.

JP 8273946 describes a planar transformer with extension leads for mounting the planar transformer with its substrate stack parallel to a printed circuit board. Extension leads are connected at one of their ends to contact points connected to the windings. The other ends of the leads are either designed for insertion mounting into holes in the printed circuit board or have small flat pads for surface mounting.

JP 08273944 describes a planar transformer with multiple extension leads for mounting on printed circuit boards.

PCT publication WO96/21935 describes a planar transformer having a single pair of core elements sandwiching a substrate stack comprising primary and secondary windings. The transformer is mounted on a printed circuit board with the substrate stack parallel to the board.

Contact between the transformer windings and the printed circuit board is made with wire extension leads having a length on the order of half the core thickness.

A publication entitled "Planar Magnetics" published by Philips Electronics N.V. in June 1994 describes the construction of planar inductive devices. A multiplicity of substrate boards, on which conductive windings are placed, are stacked together to form the coils of a planar inductive device. Contact points are placed at the edges of the boards for attaching extension leads to the coils. The substrate stack is sandwiched between the two matching elements of a ferrite core.

A planar inductive device designed as an integral part of a printed circuit board is also demonstrated in the publication. The windings of the planar inductive device are printed on the circuit board for which the planar inductive device is intended along with other components of the circuit. The two elements of a ferrite core are inserted into apertures in the circuit board to form the planar inductive device.

The use and application of planar inductive devices have been stimulated by the consistent trends in the electronics industry to miniaturization and encapsulation. To the extent allowed by technology and economics, electronic components are miniaturized and densely packaged into standardized self contained printed circuit boards.

There is a demand for inexpensive inductive device which are easily mounted on circuit boards and occupy as small an area of the circuit board surface as possible. Furthermore, in the crowded environment in which the inductive devices are mounted they should be as efficient as possible in dissipating the heat they generate. Planar inductive devices are a solution to these demands, however, their conventional implementation leaves room for improvement.

As indicated above, conventional planar inductive devices are constructed to be mounted with the planes of their coil windings parallel to the printed circuit boards. This mounting disposition maximizes the area that the planar inductive devices occupy on the circuit boards. It would be desirable to provide alternative mounting dispositions to minimize the footprint of a given planar inductive device.

When a conventional planar inductive device is mounted on a printed circuit board, the thickness of the magnetic core displaces the plane of the substrate stack from the plane of the circuit board. No part of the windings is in direct contact with the circuit board. As a result extension leads must be used to make electrical contact between the planar inductive device and the circuit board. This complicates both the manufacture of planar inductive devices and their insertion into printed circuit boards. It would be desirable to have mounting methods that do not require extension leads. Without supplementary spacing structures, conventional planar inductive devices have large parts of their surface area in direct contact with, or only slightly elevated from the surface of the printed circuit board. These parts of the surface area have restricted air flow and therefore diminished heat dissipation which must often be specially compensated for. It would be desirable to incorporate, in the design and structure of planar inductive devices, intrinsic attributes that reduce the need to provide special structures to augment heat dissipation.

Another characteristic of conventional planar inductive devices is that for a given planar inductive device the electrical parameters are not adjustable. It would be desirable to have planar inductive devices that are tunable.

SUMMARY OF THE INVENTION It is an object of one aspect of the present invention to provide methods to reduce the size of the footprint of planar inductive devices on the circuit boards on which they are mounted.

In preferred embodiments in accordance with the present invention a planar inductive device is mounted with the plane of the windings of the planar inductive device non-parallel to the printed circuit board. As the angle between the plane of the windings of the planar inductive device and the plane of the printed circuit board approaches 90 degrees the footprint of the planar inductive decreases. This reduces the space required on the board for the planar inductive device.

Preferably the angle between the plane of the windings of the planar inductive device and the plane of the circuit board is 90 degrees. Preferably this mounting disposition is maintained by fixing an edge of the core, that is perpendicular to the plane of the windings, to the circuit board. In this manner the most massive structure of the planar inductive device is self supporting and stabilized. Preferably the edge of the core that is fixed to the circuit board is flush with an edge of the substrate stack. In a preferred embodiment of the present the invention the core and the substrate stack are not rigidly fixed to each other but allow for a degree of relative movement between the two flush edges. Preferably the degree of movement is enough to allow the edge of the substrate stack to be butted flush to the circuit board after the edge of the core is fixed in place. Preferably this edge has contact points with reflowable solder for forming electrical contact between the circuit board and the coil windings.

It will be appreciated that non-parallel mountings of planar inductive devices at angles other than 90 degrees are possible and are advantageous.

It is an object of another aspect of the present invention to provide a method for exposing more of the surface area of a planar inductive device to improved air flow in order to improve its heat dissipation.

To the extent that a portion of the surface area of the planar inductive device is displaced from the circuit board, airflow adjacent to it, whether by natural or forced convection, is improved. The improved air flow significantly improves heat dissipation. In preferred embodiments of the present invention a non-parallel mounting disposition for planar inductive devices is provided, as described above. As the mounting angle between the plane of the windings of the planar inductive device and the plane of the printed circuit board increases to 90 degrees, more of the surface of the planar inductive devices is exposed to improved airflow. It is an object of another aspect of the present invention to provide for electrical contact between the circuit board and the coils of the planar inductive device without the use of extension leads. This simplifies the production of planar inductive devices. It also leads to more robust and reliable electrical connections that are simpler to make and that lend themselves to automatic assembly. In preferred embodiments of the present invention contact points which are connected to extensions of the ends of the windings, are provided at the edges of the substrate boards e.g. metalized areas on the edge of the board which are electrically connected to the extensions. Preferably the contact points are provided with reflowable material such as solder. Preferably the core and substrate boards are assembled so that the edge or edges with the contact points may be butted flush up against matching contact points on one or more printed boards, with a surface of the core attached to the printed circuit board. Permanent electrical connection between the contact points of the substrate boards and the printed circuit boards are formed by processes known to the art, such as by using conductive glue or reflow solder techniques. It will be appreciated that the structures and method for forming electrical contact between the substrate boards and a printed circuit board as described above are advantageous and applicable to the connection of a first printed circuit board having electronic components mounted on its surface, that may or may not include planar inductive devices, to a second printed circuit board. The electronic components are connected to metalized areas on the first printed circuit board for the purpose of electrical and mechanical contact. The metalized areas have extensions to edges of the first circuit board which are metalized at which they have contact points provided with reflowable material such as solder. The edge of the first printed circuit board having the contact points is butted to the surface of the second printed circuit board so that the contact points on the edge of the first circuit board are in physical contact with suitably placed matching contact points on the surface of the second printed circuit board. Permanent electrical contact between the contact point on the edge of the first circuit board and the surface of the second surface board are then made by processes known in the art such as by using conductive glue or solder reflow techniques. Mounting a first circuit board to a second circuit board as described above is generally most useful for first circuit boards which are relatively small and light in order for the first circuit board to be fixed mechanically stable to the second circuit board. Moreover, mechanical stability is enhanced if the first circuit board has a thickness on the order of or greater than 1-2 mm. It is appreciated that other means for increasing the stability of first circuit boards which are mounted to second circuit boards as described are advantageous and can readily be provided.

It is an object of another aspect of the present invention to provide for a construction method for cores of planar inductive devices that permits the flexible matching of standard core dimensions to the dimensions of substrate stacks for planar inductive devices. In preferred embodiments of the present invention, the magnetic cores of planar inductive devices are constructed from a plurality of standardized core modules. Preferably the core modules consist of a pair of suitably matched opposing elements. The core modules are combinable to form cores of different sizes and shapes in order to match the dimensions of different substrate stacks. It is an object of another aspect of the present invention to provide a planar inductive device with an adjustable core, thereby providing for tuning of the electrical characteristics of the planar inductive device. In preferred embodiments of the present invention the magnetic core of a planar inductive device is composed of a plurality of core pair modules. Core modules can be added to or removed from the core to tune the electrical characteristics of the planar inductive device. In preferred embodiments of the present invention the position of a core module is adjustable with respect to the windings of the planar inductive device. Preferably, the core can be fixed in place after positioning. The movement of the core tunes the planar inductive device.

It is an object of some aspects of the present invention to provide for a planar inductive device with an adjustable core that can be tuned after mounting on a printed circuit board. In preferred embodiments of the present invention the planar inductive device is mounted on printed circuit boards with sufficient clearance so that magnetic core modules can be added or removed from the planar inductive device without having to dismantle the planar inductive device from the circuit board. The planar inductive device and its inductive coupling to other components of the circuit board is tuned by the addition or subtraction of core modules. Preferably the planar inductive device is mounted on the printed circuit board in a vertical disposition.

In preferred embodiments of the present invention the planar inductive device is mounted on printed circuit boards with sufficient clearance so that the position of the core or part of the core with respect to the coils is adjustable. Preferably the core position is fixed in place after positioning. The movement of the core tunes the electrical characteristics of the planar inductive device and the amount of its inductive coupling with the other circuit elements on the printed circuit board.

There is thus provided a planar inductive device comprising: at least one substrate board having planar windings formed thereon; and a core, arranged with respect to the windings, so as to form a magnetic path between the primary and secondary windings, wherein the at least one board is provided with contact connectors on an edge thereof for edge mounting the at least one board.

There is further provided, in accordance with a preferred embodiment of the invention, a planar inductive device comprising: at least one substrate board having an edge in a first direction and also having planar windings formed thereon; and a core, arranged with respect to the windings, so as to form a magnetic path between the windings, the core having an extent in said first direction which is substantially the same as that of the edge

There is further provided, in accordance with a preferred embodiment of the invention, a planar inductive device comprising: at least one substrate board having primary and secondary planar windings formed thereon; and a plurality of cores arranged with respect to the windings so as to form a magnetic path between the windings. Preferably, cores may be added to or removed from the core. Preferably, the position of one or more of the cores is adjustable.

In a preferred embodiment of the invention, the stack comprises contacts electrically connected to ends of said windings. Preferably, the contacts comprise contacts for edge mounting of the at least one board. Preferably, the contacts comprise metalization of the edge of the at least one board and the contacts are adapted for direct connection to a mother board. Preferably, the contacts comprise reflow solder contacts or are adapted for use with conductive adhesive.

In a preferred embodiment of the invention, the at least one board comprises a stack of boards. There is further provided, in accordance with a preferred embodiment of the invention, a method for mounting planar inductive devices having windings disposed on at least one substrate and a core onto a circuit board comprising: fixing the core to the circuit board with the substrate non-parallel with the board; and forming electrical contact between the windings and the circuit board. In a preferred embodiment of the invention, fixing the core comprises fixing a surface of the core that is not parallel to the windings of the planar inductive device to the circuit board. In a preferred embodiment of the invention, fixing the core comprises fixing at least one surface of the core, which is parallel to the windings, to the circuit board.

In a preferred embodiment of the invention fixing the core comprises fixing a surface of the core which is perpendicular to the windings to the circuit board such that the windings are substantially perpendicular to the circuit board.

In a preferred embodiment of the invention, fixing the core comprises gluing the core to the circuit board. In a preferred embodiment of the invention, forming electrical contact comprises edge mounting the substrate on the circuit board.

In a preferred embodiment of the invention, forming electrical contact comprises metalizing an edge of the at least one substrate board. In a preferred embodiment of the invention, forming electrical contact comprises directly forming electrical contact between the metalized edge of the at least one substrate board and a mother board. Preferably, forming electrical contact between the metalized edge of the at least one substrate board and a mother board comprises reflowing solder or using conductive adhesive. There is further provided, in accordance with a preferred embodiment of the invention, a method for tuning a planar inductive device having windings formed on a substrate and a core forming a magnetic circuit coupling the windings comprising: mounting a planar inductive device on a circuit board in a manner which allows for adjustment of the core; and adjusting the core of the planar inductive device.

In a preferred embodiment of the invention adjusting the core comprises, changing the volume of the core. In a preferred embodiment of the invention, wherein the core comprises a plurality of core elements, changing the volume of the core comprises changing the number of core elements in the core. Alternatively or additionally, adjusting the core comprises changing the position of the core in the windings.

There is further provided a planar inductive device mounted on a printed circuit board comprising: at least one substrate board having planar windings formed thereon and also having an edge on which are formed conducting contacts that are connected to the windings; and a core, arranged with respect to the windings, so as to form a magnetic path between the windings; wherein the at least one board is mounted on the printed circuit board such that the contacts on the edge are electrically connected to conductive contacts on the printed circuit board and the edge is flush with the surface of the printed circuit board.

There is further provide a method for mounting onto a printed circuit board a planar inductive device having a core and planar windings disposed on at least one substrate, where the substrate has an edge, comprising: forming electrical contact between the windings and contact areas on the printed circuit board; and mounting the planar inductive device on the printed circuit board such that the edge is flush with the surface of the printed circuit board while maintaining said electrical contact. The invention will be more clearly understood by reference to the following description of preferred embodiments thereof, in conjunction with the figures in which:

BRIEF DESCRIPTION OF FIGURES Fig. 1 shows a conventional planar transformer mounted on a printed circuit board; Fig. 2 shows a planar transformer in accordance with a preferred embodiment of the present invention mounted on a printed circuit;

Fig. 3 shows a planar transformer, having a "T" cross-section, in accordance with a prefeπed embodiment of the present invention, where the transformer is inserted into an aperture of a printed circuit board; and

Fig. 4 shows an exploded view of the construction of a planar transformer in accordance with a preferred embodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Fig. 2 shows a planar transformer 32, in accordance with a preferred embodiment of the present invention, mounted on a printed circuit board 202. It comprises a stack 34 of substrate boards on which the transformer windings (not shown) are located. Stack 34 is sandwiched between two opposable elements 38 and 40 of a magnetic core 36, preferably a ferrite core. One of the edges of stack 30 and an edge of core 36 are in direct flush contact with printed circuit board 202. The edge surface of the core is preferably glued to the printed circuit board for mechanical stability. The planes of the transformer windings are in a vertical mounting, disposed at 90 degrees to the plane of the circuit board. The dimensions of core 36 and stack 34 are such that, when they are assembled together, an edge of the stack is flush with an edge of the core. However, core 36 and stack 34 are preferably not fixed rigidly one to the other. They are preferably constructed such that a certain degree of relative movement of the flush edges with respect to each other is possible.

This allows for the edge of the stack to be butted flush to the circuit board after the edge of the core is fixed in place, despite iπegularities in the edges or in the printed circuit board surface and without requiring production of the transformer to a close mechanical tolerance.

The edge surface of the stack, which is in flush contact with the circuit board, has a plurality of contact points for input and output to the transformer. Two of them, 42 and 44, are shown and are indicative of the construction of the others. Contact points 42 and 44 are connected to lead elements 46 and 48 respectively of the windings. Preferably lead elements 46 and 48 are continuous integral parts of the windings (not shown)and are formed during the process of forming the coils. Preferably contact points 42 and 44 are provided with reflowable material for making permanent electrical contact with the circuit board. Alternatively, contact may be made using a conductive epoxy or other conductive glue.

The vertical mounting disposition of planar transformer 32 reduces the footprint of the transformer in comparison to other mounting dispositions.

The vertical mounting disposition also improves heat dissipation from transformer 32 by improving air flow over its surface. The vertical mounting disposition increases the proportion of the surface area of the transformer that is displaced from the circuit board. This displacement aids in preventing the build up of insulating stagnant air pockets adjacent to the surfaces. This improvement is effected without the need for adding special structures to either the circuit board or to the transformer core or substrate stack.

Reliability of contact to the circuit board is improved by doing away with the need for the added extension leads of conventional planar transformers.

It is appreciated that non-parallel mountings of transformer 32 at dispositions other than 90 degrees are possible and advantageous. The faces of ferrite core 36 in Fig. 2 are perpendicular to each other. Core 36 can, however, be formed so that the edge surface of core 36 which is glued to printed circuit board 202 is not perpendicular to the surfaces of core 36 which are adjacent to it. This will result in core 36 being tilted out of the vertical when it is glued to printed circuit board 202. The edge of stack 34 that is in contact with circuit board 202 is formed so that it is parallel and flush with the edge of the core that is glued to circuit board 202, in order to accommodate the tilt of core 36 out of the vertical. It is appreciated that still other constructions of core 36 and stack 34 are possible and will achieve non-parallel mountings of transformer 32 at other than 90 degrees.

Fig. 3 shows planar transformer 48, according to a preferred embodiment of the present invention, mounted on a printed circuit board 204. Planar transformer 48 is mounted in an aperture socket in the form of a clearance hole 50 formed in circuit board 204. Stack 52 is made of a plurality of substrate boards 54-60. Substrate boards 54-60 and consequently the Substrate stack 52 are T shaped. Opposable elements 66 and 68 of a ferrite core 64 sandwich substrate stack 52 between them. Preferably the top edge of core 64 is flush with the top edge of the T of stack 52. Preferably the bottom edge of core 64 is flush with the bottom edge of the stem of the T of stack 52. Aperture socket 50 has dimensions large enough to receive the stem of the T of stack 52 and the part of core 64 which sandwiches it. The top of the T is too wide to pass through the socket since it is formed with two extensions, 70 and 72, which protrude from either side of the stem of the T. The planar transformer is inserted up to the bottom edges of the extensions 70 and 72. The bottom edges of extensions 70 and 72 are provided with a multiplicity of input and output contact points to the transformer windings. Two of these, 74 and 76, are shown in the figure. The contact points are connected to the lead elements (not shown) of the windings (not shown) in the same manner as the contact points of transformer 32 of Fig. 2. Transformer core 64 is preferably fixed in place by gluing it to the edge of the socket aperture 50.

As with planar transformer 32 of Fig. 2, planar transformer 48 of Fig. 3 is mounted in a vertical disposition. It leaves a small footprint on the circuit board and improves the air flow to the transformer's surface. The mounting method shown in Fig. 3 additionally permits adjustment of the amount by which the transformer protrudes from either side of the circuit board.

It is appreciated that non-parallel mountings of transformer 48, at other than 90 degrees, are possible and advantageous. Stack 52 is generally very thin. When transformer 48 is inserted into socket aperture 50 of printed circuit board 204 the transformer can be rotated out of the vertical about the axis which is the line of contact between the thin edge of stack 52 and printed circuit board 204. Core 64 can then be fixed in place by gluing to socket aperture 50. If stack 52 is thick the angle between the faces of stack 52 and the edge surfaces of stack 52 that are in contact with circuit board 204 can be constructed to be different from 90 degrees. This permits non-parallel mountings of transformer 48 at other than 90 degrees. It is appreciated that still other constructions of transformer 48 that permit non parallel mountings are possible and advantageous.

It is also appreciated that sockets of form and construction different from socket aperture 50 are possible and advantageous. For example, the edges of socket aperture 50 could be provided with a covering of resilient material so that when core 64 is inserted into aperture 50 the resilient material presses onto the surface of core 64 holding core 64 resiliently in place. This would obviate the need of securing the core in place by gluing. It is appreciated that still other sockets constructions are possible and advantageous.

Fig. 4 is an exploded illustration showing the structure of a planar transformer 80 produced in accordance with a preferred embodiment of the present invention. Planar transformer 80 has a magnetic core 82 which is composed of a plurality of ferrite core modules. Each module is composed of a pair of matching elements. The module pair elements are labeled: 84 and 94, 86 and 96, 88 and 98, 90 and 100. The transformer further comprises a plurality of insulating substrate boards 102, 104, 108, and 110.

Insulating substrate boards 102, 104, 108, 110 have respective conductive spiral windings 118 to 124 on their surfaces. Boards 102 and 104 are stacked together with windings 118 and 120 connected at vias 126 and 128 using materials and procedures known in the art. The joined windings become one coil of the transformer. Input and output connections to the coil are made at a pair of contact points 130 and 132 at the ends of a pair of lead extensions 134 and 136. The method for making the connections is illustrated in Fig. 2 and described in the discussion of that Fig. Boards 108 and 110 are assembled together in the same way to form the second coil of the transformer. The two coils are sandwiched and adhered together to form the substrate stack of the transformer. Alternatively, the adjacent stacks are formed with coil portions of primary and scondary transformer windings. Thus, for example, odd stacks would be interconnected to form one winding and even windings would be interconnected to form the other winding. For a transformer having more than two windings, similar adjacent or staggered interconnections may be used.

The dimensions of each of the substrate boards are preferably substantially identical and each of the boards has a substantially identical set of clearance apertures and two edge cutouts which are indicated, for board 104, as 112, 114 and 116 respectively. The two elements of each ferrite core module 84 and 94 through 90 and 100 are inserted into aperture 112 and edge cutouts 114 and 116 of the stack from opposing sides to a depth at which they contact. While in contact, the two elements of each core module pair 84 and 94 through 90 and 100 are adhered together using appropriate adhesives. The dimensions of aperture 112 and edge cutouts 114 and 116 are large enough for all the core modules 84 and 94 through 90 and 100 to fit in together to form core 82. The fit between core 82 and the stack is preferably not tight.

Dimension 138 of the core modules and dimension 140 of the substrate boards are preferably equal. As a result, when the core 82 and the substrate stack are assembled together their top and bottom edges are flush but some play exists. Sufficient tolerance is thereby provided for mounting the transformer so that after the core edge is adhered to the circuit board the stack edge can also be positioned in good flush contact with the circuit board. This enables the forming of accurate and reliable electrical contact to the transformer despite inaccuracies in the mounting of the core or of irregularities in the surface of the circuit board or the edge of the stack that might otherwise prevent this. The modular construction of core 82 of Fig. 4 illustrates a method of adapting the size of core 82 to different aperture and edge cutout dimensions by the addition or removal of standard core modules. It is appreciated that core module shapes and dimensions other than those shown in Fig. 4 for core module pairs 84 and 94 through 90 and 100 are possible and advantageous. Different module shapes expand the applicability of the modular core design to a greater variety of core geometries.

In Fig. 4 stack aperture 112 and edge cutouts 114 and 116 accommodate up to a maximum of four ferrite core module pairs. By inserting more or fewer modules, the electrical characteristics of the transformer can be tuned. Also, modules can be added to or removed from the transformers after the transformer is mounted.

When fewer than four modules are inserted into the stack, the modules are movable in the stack aperture. By adjusting the positions of the modules the transformer can be tuned. After optimal positioning the modules can be fixed in place by gluing.

It is understood that while the invention has been described in conjunction with planar transformer embodiments, the invention is equally applicable to planar inductors or other planar inductive devices. Furthermore, some aspects of the invention are applicable to mounting of non inductive devices. For example, the direct edge mounting of a printed circuit board, as described above is applicable to mounting a wide variety of printed circuit boards.

The present invention has been described utilizing a non-limiting detailed description of preferred embodiments thereof. However, the full scope of the invention is not limited by the details of the description but is defined by the following claims.

Claims

1. A planar inductive device comprising: at least one substrate board having planar windings formed thereon; and a core, arranged with respect to the windings, so as to form a magnetic path between the windings, wherein the at least one board is provided with contacts on an edge thereof for edge mounting the at least one board.

2. A planar inductive device comprising: at least one substrate board having an edge in a first direction and also having planar windings formed thereon; and a core, arranged with respect to the windings, so as to form a magnetic path between the windings, the core having an extent in said first direction which is substantially the same as that of the edge.

3. A planar inductive device comprising: at least one substrate board having planar windings formed thereon; and a plurality of cores arranged with respect to the windings so as to form a magnetic path between the windings.

4. A planar inductive devices according to claim 3 wherein cores may be added to or removed from the core.

5. A planar inductive device according to claim 3 wherein the position of one or more of the cores is adjustable.

6. A planar inductive device according to claim 2 or claim 3 wherein the stack comprises contacts electrically connected to ends of said windings.

7. A planar inductive device according to claim 6 wherein the contacts comprise contacts for edge mounting of the at least one board.

8. A planar inductive device according to claims 1 or 6 or 7 wherein the contacts comprise metalization on the edge of the substrate board and the contacts are adapted for direct connection to a mother board.

9. A planar inductive device according to claim 8 wherein the contacts comprise reflow solder contacts.

10. A planar inductive device according to claim 8 wherein the contacts comprise contacts for use with conductive adhesive.

11. A planar inductive device according to any of the preceding claims where the planar inductive device is a planar transformer.

12. A planar inductive device according to any of claims 1 through 10 where the planar inductive device is a planar inductor.

13. A planar inductive device according to any of the preceding claims wherein the at least one board comprises a stack of boards.

14. A method for mounting a planar inductive device having planar windings disposed on at least one substrate and a core onto a circuit board comprising: fixing the core to the circuit board with the substrate non-parallel with the board; and forming electrical contact between the windings and the circuit board.

15. A method according to claim 14, wherein fixing the core comprises fixing a surface of the core that is not parallel to the windings of the planar inductive device, to the circuit board.

16. A method according to claim 14, wherein fixing the core comprises fixing at least one surface of the core, which is parallel to the windings, to the circuit board.

17. A method according to claim 14 wherein fixing the core comprises fixing a surface of the core which is perpendicular to the windings to the circuit board such that the windings are substantially perpendicular to the circuit board.

18. A method according to any of claims 14-17 wherein fixing the core comprises gluing the core to the circuit board.

19. A method according to any of claims 14-18, wherein forming electrical contact comprises edge mounting the substrate on the circuit board.

20. A method according to claim 19 wherein forming electrical contact comprises metalizing an edge of the at least one substrate board.

21. A method according to claim 20 wherein forming electrical contact comprises directly forming electrical contact between the metalized edge of the at least one substrate board and a mother board.

22 A method according to claim 21 wherein forming electrical contact comprises reflowing solder.

23 A method according to claim 21 wherein forming electrical contact comprises gluing the metalized edge to the mother board with conductive adhesive.

24. A method for tuning a planar inductive device having windings formed on a substrate and a core forming a magnetic circuit coupling the windings comprising: mounting a planar inductive device on a circuit board in a manner which allows for adjustment of the core; and adjusting the core of the planar inductive device.

25. A method according to claim 24 wherein adjusting the core comprises, changing the volume of the core.

26. A method according to claim 24 wherein the core comprises a plurality of core elements, changing the volume of the core comprises changing the number of core elements in the core.

27. A method according to any of claims 24-26 wherein adjusting the core comprises changing the position of the core in the windings.

28. A method according to any of claims 14 - 27 where the planar inductive device is a planar transformer.

29. A method according to any of claims 14-27 where the planar inductive device is a planar inductor.

30. A planar inductive device mounted on a printed circuit board comprising: at least one substrate board having planar windings formed thereon and also having an edge on which are formed conducting contacts that are connected to the windings; and a core, arranged with respect to the windings, so as to form a magnetic path between the windings; wherein the at least one board is mounted on the printed circuit board such that the contacts on the edge are electrically connected to conductive contacts on the printed circuit board and the edge is flush with the surface of the printed circuit board.

31. A method for mounting onto a printed circuit board a planar inductive device having a core and planar windings disposed on at least one substrate, said substrate having an edge, comprising: forming electrical contact between the windings and contact areas on the printed circuit board; and mounting the planar inductive device on the printed circuit board such that the edge is flush with the surface of the printed circuit board while maintaining said electrical contact.